308 Prof. J. Joly on the Apophorometer* 



of the substance. An instance in point seems to be forth- 

 coming in the case of the telurides dealt with above. 



With further experience there will be more to be said 

 about the uses of this instrument. I hope to deal with its- 

 applications in a more systematic way in another paper. 

 The temperature at which the sublimates are given off 

 should be determined. In my earlier work, before I used 

 the expansion of platinum (as in the meldometer) and 

 employed carbon or platinum for the hob, I determined 

 temperature by optical pyrometry or by electrical resistance* 

 The first method has the fatal objection, as regards the 

 apophorometer, that some of the most useful temperatures 

 are sub-luminous. The second is very troublesome. In 

 the case of the apophorometer I find the readings of the 

 amperemetre afford the temperature to a sufficient degree 

 of accuracy. It is only requisite to use in every case 

 platinum or carbon of the same length and cross-section. 

 In the case of platinum this, I find, presents no difficulties. 

 By observation of the melting of a few substances of known 

 melting-point, placed on the hob under exactly the same' 

 conditions as obtain when an ordinary experiment is being 

 made, and simultaneous observations of the current, a 

 graph is readily constructed which gives 'the approximate 

 temperature corresponding to any strength of current. 



The uses of the apophorometer are not by any means 

 restricted to gravimetric measurements. All that class of 

 work which I formerly assigned to the meldometer and 

 N\hich does not call for microscopic observation and accurate 

 temperature readings, can be effected by its means. The 

 brief summary of this work, which appears in a former 

 paper *, may be reprinted here ; for although other work on 

 the meldometer has been since carried out in my laboratory 

 and elsewhere, this subsequent work has, so far as I know,, 

 been largely restricted to the revision of melting-points. 

 The earlier summary of qualitative work is, I think, still 

 fairly comprehensive. In what follows we may read at 

 pleasure " apophorometer " for " meldometer." 



" Sublimation. 



" This apparatus affords a means of obtaining sublimates 

 much transcending the blowpipe (used either with carbon 

 or aluminium) in delicacy, range, and purity. Sublimates 



* Joly, " The Uses of the Meldometer," Proc. Royal Irish Academy, 

 3rd ser. vol. xi. No. 1, May 1891, p. 44 et seq. 



